Speaker
Description
We present an experimentally and analytically rigorous reexamination of the urethane addition reaction under vibrational strong coupling (VSC) initially reported by Ahn & Simpkins in 2023. Our current results indicate no modification of chemical reaction rates between cavity-coupled and uncoupled systems. The specific causes for the previously measured differences are under investigation. However, we have uncovered two important measurement features that must be accounted for to make reliable measurements of this sort. First, we find, counterintuitively, that the reaction rates extracted from cavity-coupled transmittance spectra can be more reliable than those obtained from extracavity (i.e., control) reaction spectra, because pathlength information is more easily and readily accessible in the cavity spectra. Changes in pathlength caused by solution injection and the subsequent relaxation can result in systematic errors of the extracted concentration depending on the sign and magnitude of the change. We demonstrate that using an expanded solution dielectric function, which provides pathlength information encoded in solvent vibrational bands, reduces the disparity between extracavity and cavity rates. Secondly, we investigate the effect of pathlength nonuniformity on reaction rates extracted from cavity-coupled spectra and find that the analytical approach used by Ahn & Simpkins which mimics spatial/temporal broadening of cavity modes by artificially reducing the simulated quality factor can systematically overestimate molecular concentration. We show that when the simulated cavity transmittance is modeled to reflect the true underlying pathlength distribution, the correct molecular concentration is obtained. When pathlength instability and nonuniformity are accounted for using these methods, the difference between cavity and extracavity reaction rates (previously attributed to modified chemistry under VSC) vanishes.